Notes / Test & Debug Instruments
Soldering and rework
SMD soldering, flux, hot air, solder wick. The hand skill to fix a prototype is part of an embedded developer's basics too.
Tools
| Tool | Use |
|---|---|
| Temperature-controlled iron (330 to 370 °C) | Chip resistors, pin soldering |
| Flux | Helps solder flow, prevents bridges |
| Solder wick (desoldering braid) | Soaking up leftover solder |
| Hot-air station | Removing QFNs and multi-pin parts |
| Tweezers, magnifier / microscope | 0402, fine pitch |
SMD soldering technique
- Chip parts: put solder on one pad first, slide the part in and fix it, then solder the other side
- QFP (fine-pitch IC): fix the position with two diagonal pins, apply plenty of flux, then sweep the iron along the row of pins (drag soldering). Remove bridges with solder wick
- QFN, BGA: need hot air or reflow
Rework
- Heat a wrongly fitted part with hot air and lift it off, then flatten the pads with solder wick
- Modify the circuit with thin enamelled wire (jumper wire). When cutting a trace with a knife, confirm with a multimeter that it is cut
Safety
Extract flux fumes with a fume extractor, and wash your hands after soldering. Lead-free solder has a higher melting point, so the temperature has to be a little higher.